A fundamental process carried out by all viruses is the assembly of the virion. A detailed understanding of this process will be invaluable of effective antiviral strategies as well as providing insight into basic macromolecular process. The proposed project will investigate the assembly of enveloped viruses. The research will span two families of structurally related viruses: the flaviviruses and togaviruses. The flaviviruses comprise a family of plus-strand RNA viruses, many of which cause significant disease in humans. This proposal will focus on yellow fever virus and hepatitis C virus. In addition, our study of togavirus assembly will be devoted to rubella virus, the sole member of the rubrivirus genus. We propose to investigate the process by which these viruses assembly their inner nucleocapsid core and the subsequent association of the core with transmembrane glycoproteins. A multi- disciplinary approach will be employed to investigate this assembly process. This approach will entail the use of molecular genetics, biochemistry and structural techniques to probe the mechanism of virus assembly and to ultimately describe the process in atomic detail. In collaboration with Tim Baker's laboratory, we will use cryo electron microscopy and image reconstructions to Rossmann's laboratory, we will carry out crystallographic experiments to determine the atomic structure of the nucleocapsid proteins and in vitro assembled nucleocapsid cores. In parallel, we will use NMR techniques, in collaboration with Carol Post, to probe the structure of capsid proteins. We will carry out biochemical studies on purified capsid proteins produced in E. coli. These studies will examine the processes of capsid-capsid interaction, capsid-nucleic acid interaction, core assembly and capsid-glycoprotein interaction. We will also perform molecular genetic studies on yellow fever and rubella to examine structure-function relationships in these capsid proteins and their role in the virus life cycle. The proposed research will advanced our knowledge of virus assembly, macromolecular interactions, and serve as a paradigm for the molecular mechanism of virus and cellular budding.